1. Field of the Invention
The present invention relates to a high-speed semiconductor device, more particularly to a hot electron transistor (HET) device which includes a heterojunction emitter, base, collector, and a superlattice means between the emitter and the base.
2. Description of the Related Art
The principle of an HET has long been known (C. A. Mead, Proc. IRE48, 359, 1961). This old HET, however, was structured by stacked metal and oxide layers, and thus could not be applied to actual semiconductor devices.
Recently, due to advances in semiconductor processing technology, such as molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD), new HET's having, for example, n-type galliumarsenic (GaAs) layers instead of the above metal layers and aluminum-gallium-arsenic (AlGaAs) layers instead of the above oxide layers have been developed (see, e.g., "Characterization of Double Heterojunction GaAs/AlGaAs Hot Electron Transistors", N. Yokoyama, et al. PROCEEDINGS OF THE IEEE INTERNATIONAL ELECTRON DEVICES MEETING, Dec. 1984, pp 532 to 535).
These newer HETs, however, suffer from low current amplification.